ISO11172ANNEXEFG教學教材

1、Good is good, but better carries it.精益求精，善益求善。ISO11172ANNEXEFG-3-ANNEXE(informative)BITSENSITIVITYTOERRORS3-E.1.GeneralThisparagraphindicatesthesensitivityofindividualbitstorandomerrorsifapplicationspecificerrorprotectionisneeded.Thissensitivityisgivenforeachbitbyavaluefrom0to5,indicatingtheamountof

2、degradationresultingfromoneisolatederror:5catastrophic4veryannoying3annoying2slightlyannoying1audible0insensitiveThevaluesarenottheresultsofprecisemeasurements,rathertheyrelyuponknowledgeofthecodec.Theyassumetheerrordetectionschemeisnotinuse.Somefieldsinthebitstreamdonothaveafixedlength.Allbitsinthi

3、sfieldsareratedforerrorsensitivity,evenifnotinuse.(Foralllayers,theheaderinformationisconsideredtohavethehighestsensitivity).3-E.2.LayersIandIIParameters#bitsensitivityBitallocationallbits5Scalefactorsselectinformationallbits5Scalefactors5(msb)4443423120(lsb)1Subbandsamples(*)8-16(msb)35-723,41(lsb)

4、0-20(*)accordingtothebitallocation3-E.3.LayerIIIParameters#bitsensitivityScf_siallbits5Part2/3_lengthallbits4Big_valuesallbits3Global_gainallbits5Scalefactor_selectallbits5Blocksplit_flagallbits5Block_typeallbits4Switch_frequencyallbits4Table_selectallbits5Region_adress1allbits3Region_adress2allbits

5、3extension_bits(ifpresent)allbits0Preflag02Scalefac_scale02Count1table_select03Subblock_gain2(msb)4130(lsb)2Scalefac(*)3(msb)3(2)23(2)12(1)0(lsb)2(1)Huffmancodes(*)0.n-13-0(*)thescalefaclengthdependsonscalefac_select.Thebitsensitivityvaluesrefertothescalefac_scalevalue1(if0thevalueisinparenthesis).(

6、*)IfnisthenumberofbitsforHuffmancodinginoneblockthebitsensivitydecreaseslinearlyfrom3to0asthebitnumbervariesfrom0upton,(fromlowtohighfrequency).Note:RearrangementoftheHuffmancodedvalues:TogetbetterimpliciterrorrobustnessforthelowfrequencypartofthespectrumtheHuffmancodedvaluescanbetransmittednotinthe

7、irlogicalorder,butinaninterleavedfashion.Ifmax_hlenisthemaximumlengthofaHuffmancodewordoverthetableswhichareusedtocodetheparticularblockandnisthenumberofbitsusedforHuffmancodingofdataintheblock(notframe),thenint(n/max_hlen)slotsarefilledwiththefirstcodewords,beginningfromlowfrequencies.Theremainingc

8、odewordsarefilledintotheremainingplace,againarrangedfromlowtohighfrequencies.Afterbitinterleaving,thebitsensivityofbitk+i*int(n/max_hlen)decreaseslinearlyfrom3to0askvariesfrom0uptoint(n/max_hlen)-1,wherei=0,.,max_hlen-1,andnisthenumberofbitsforHuffmancodinginoneblock.ThisistherecommendedpracticeforL

9、ayerIIIdataforallchannelswhereerrorrobustnessisimportant.3-ANNEXF(informative)ERRORCONCEALMENTAnoptionalfeatureofthecodedbitstreamistheCRCwordwhichprovidessomeerrordetectionfacilitytothedecoder.TheHammingdistanceofthiserrordetectioncodeisd=4,whichallowsforthedetectionofupto3singlebiterrorsorforthede

10、tectionofoneerrorburstofupto16bitlength.Theamountandthepositionoftheprotectedbitswithinoneencodedaudioframegenerallydependsonthelayer,themode,datarate,andsamplingfrequency.Thiscanbeusedtocontrolanerrorconcealmentstrategyinordertoavoidsevereimpairmentsofthereconstructedsignalduetoerrorsinthemostsensi

11、tiveinformation.Somebasictechniquescanbeusedforconcealment,forinstanceinformationsubstitution,ormuting.Asimplesubstitutiontechniqueconsists,whenanerroneousframeoccurs,ofreplacingitbythepreviousone(iferrorfree).3-ANNEXG(informative)JOINTSTEREOCODING3-G.1.IntensityStereoCodingLayerI,IIAnoptionaljoints

12、tereocodingmethodusedinLayersIandIIisintensitystereocoding.Intensitystereocodingcanbeusedtoincreasetheaudioqualityand/orreducethebitrateforstereophonicsignals.Thegaininbitrateistypicallyabout10to30kbit/s.Itrequiresnegligibleadditionaldecodercomplexity.Theincreaseofencodercomplexityissmall.Theencoder

13、anddecoderdelayisnotaffected.Psychoacousticresultsindicatethatathighfrequencies(aboveabout2kHz)thelocalizationofthestereophonicimagewithinacriticalbandisdeterminedbythetemporalenvelopeandnotbythetemporalfinestructureoftheaudiosignal.Thebasicideaforintensitystereocodingisthatforsomesubbands,insteadof

14、transmittingseparateleftandrightsubbandsamplesonlythesum-signalistransmitted,butwithscalefactorsforboththeleftandrightchannels,thuspreservingthestereophonicimage.Flowdiagramsofastereoencoderanddecoder,includingintensitystereomode,areshowninFigure3-G.1GENERALSTEREOENCODERFLOW-CHARTandFigure3-G.2GENER

15、ALSTEREODECODERFLOW-CHART.First,anestimationismadeoftherequiredbitrateforbothleftandrightchannel.Iftherequiredbitrateexceedstheavailablebitrate,therequiredbitratecanbedecreasedbysettinganumberofsubbandstointensitystereomode.Dependingonthebitrateneeded,subbands16to31,12to31,8to31,or4to31canbesettoint

16、ensitystereomode.Forthequantizationofsuchcombinedsubbands,thehigherofthebitallocationsforleftandrightchannelisused.Theleftandrightsubbandsignalsofthesubbandsinjointstereomodeareadded.Thesenewsubbandsignalsarescaledinthenormalway,buttheoriginallydeterminedscalefactorsoftheleftandrightsubbandsignalsar

17、etransmittedaccordingtothebitstreamsyntax.Quantizationofcommonsubbandsamples,codingofcommonsamples,andcodingofcommonbitallocationareperformedinthesamewayasinindependentcoding.3-G.2.MS_StereoandIntensityStereoCodingLayerIIIInLayerIIIacombinationofms_stereomode(sum/difference)andintensitystereomodecan

18、beused.1)MS_stereoswitchingMS_stereomodeisswitchedonifinjointstereomodecondition0.8*istrue.ThevaluesrliandrricorrespondtotheenergiesoftheFFTlinespectrumoftheleftandrightchannelcalculatedwithinthepsychoacousticmodel.2)MS_stereoprocessing-MSmatrixInMS_stereomodethevaluesofthenormalizedmiddle/sidechann

19、elMi/Siaretransmittedinsteadoftheleft/rightchannelvaluesLi/Ri:Mi=andSi=-LimitationofSichannelbandwithAllSivaluesabovethehighestscalefactorbandaresettozero.-SparsingofSichannelIneveryscalefactorbandsballpairsofsmallvalues(Si,Si+1)aresettozero:if(Si2+Si+12)ssb*(Li2+Li+12+Ri2+Ri+12)Si=0;Si+1=0;Thefollo

20、wingdifferencechannelthresholdcoefficientsapplytothescalefactorbandsforblocktype!=2(longMDCTtransforms):sb0123456789-ssb0.00.00.00.00.000.100.10sb1011121314151617181920-ssb00.400.500.600.700.800.901.001.503)Intensitystereoprocessing-CalculationofintensitystereopositionForeachscalefactorbandsbcodedinintensitystereothefollowingstepsareexecute